This study presents a computational fluid dynamics (CFD) model that examines the impact of phase change materials (PCMs) on the thermal resistance of expanded polystyrene particles used for concrete weight reduction and the environmental thermal behavior of construction buildings. The present study describes the design of the PCM among the roof and concrete wall layer for solar energy storage in structures and efficiency gains in thermal systems. Utilizing CFD analysis, the experiment was carried out utilizing a 3D model that was optimized per mass unit over a limited range of temperatures. The numerical model exhibited a high degree of similarity to the experimental results; hence, it can be employed to assess the performance of the construction system as a storage unit in various configurations. The models, the outcomes of the simulation, are linked with experimental value. The findings indicate that the implementation of PCM stabilizes temperatures, resulting in a 28% reduction in energy consumption compared to systems without PCM. © 2025 Elsevier B.V., All rights reserved.